Commit | Line | Data |
38bf2a25 |
1 | |
2 | package Class::MOP::Attribute; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
7 | use Class::MOP::Method::Accessor; |
8 | |
9 | use Carp 'confess'; |
10 | use Scalar::Util 'blessed', 'weaken'; |
11 | use Try::Tiny; |
12 | |
13 | our $AUTHORITY = 'cpan:STEVAN'; |
14 | |
15 | use base 'Class::MOP::Object', 'Class::MOP::Mixin::AttributeCore'; |
16 | |
17 | # NOTE: (meta-circularity) |
18 | # This method will be replaced 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 |
24 | # meta-objects. |
25 | # - Ain't meta-circularity grand? :) |
26 | sub new { |
27 | my ( $class, @args ) = @_; |
28 | |
29 | unshift @args, "name" if @args % 2 == 1; |
30 | my %options = @args; |
31 | |
32 | my $name = $options{name}; |
33 | |
34 | (defined $name) |
35 | || confess "You must provide a name for the attribute"; |
36 | |
37 | $options{init_arg} = $name |
38 | if not exists $options{init_arg}; |
39 | if(exists $options{builder}){ |
40 | confess("builder must be a defined scalar value which is a method name") |
41 | if ref $options{builder} || !(defined $options{builder}); |
42 | confess("Setting both default and builder is not allowed.") |
43 | if exists $options{default}; |
44 | } else { |
45 | ($class->is_default_a_coderef(\%options)) |
46 | || confess("References are not allowed as default values, you must ". |
47 | "wrap the default of '$name' in a CODE reference (ex: sub { [] } and not [])") |
48 | if exists $options{default} && ref $options{default}; |
49 | } |
50 | if( $options{required} and not( defined($options{builder}) || defined($options{init_arg}) || exists $options{default} ) ) { |
51 | confess("A required attribute must have either 'init_arg', 'builder', or 'default'"); |
52 | } |
53 | |
54 | $class->_new(\%options); |
55 | } |
56 | |
57 | sub _new { |
58 | my $class = shift; |
59 | |
60 | return Class::MOP::Class->initialize($class)->new_object(@_) |
61 | if $class ne __PACKAGE__; |
62 | |
63 | my $options = @_ == 1 ? $_[0] : {@_}; |
64 | |
65 | bless { |
66 | 'name' => $options->{name}, |
67 | 'accessor' => $options->{accessor}, |
68 | 'reader' => $options->{reader}, |
69 | 'writer' => $options->{writer}, |
70 | 'predicate' => $options->{predicate}, |
71 | 'clearer' => $options->{clearer}, |
72 | 'builder' => $options->{builder}, |
73 | 'init_arg' => $options->{init_arg}, |
74 | exists $options->{default} |
75 | ? ('default' => $options->{default}) |
76 | : (), |
77 | 'initializer' => $options->{initializer}, |
78 | 'definition_context' => $options->{definition_context}, |
79 | # keep a weakened link to the |
80 | # class we are associated with |
81 | 'associated_class' => undef, |
82 | # and a list of the methods |
83 | # associated with this attr |
84 | 'associated_methods' => [], |
85 | # this let's us keep track of |
86 | # our order inside the associated |
87 | # class |
88 | 'insertion_order' => undef, |
89 | }, $class; |
90 | } |
91 | |
92 | # NOTE: |
93 | # this is a primative (and kludgy) clone operation |
94 | # for now, it will be replaced in the Class::MOP |
95 | # bootstrap with a proper one, however we know |
96 | # that this one will work fine for now. |
97 | sub clone { |
98 | my $self = shift; |
99 | my %options = @_; |
100 | (blessed($self)) |
101 | || confess "Can only clone an instance"; |
102 | return bless { %{$self}, %options } => ref($self); |
103 | } |
104 | |
105 | sub initialize_instance_slot { |
106 | my ($self, $meta_instance, $instance, $params) = @_; |
107 | my $init_arg = $self->{'init_arg'}; |
108 | |
109 | # try to fetch the init arg from the %params ... |
110 | |
111 | # if nothing was in the %params, we can use the |
112 | # attribute's default value (if it has one) |
113 | if(defined $init_arg and exists $params->{$init_arg}){ |
114 | $self->_set_initial_slot_value( |
115 | $meta_instance, |
116 | $instance, |
117 | $params->{$init_arg}, |
118 | ); |
119 | } |
120 | elsif (exists $self->{'default'}) { |
121 | $self->_set_initial_slot_value( |
122 | $meta_instance, |
123 | $instance, |
124 | $self->default($instance), |
125 | ); |
126 | } |
127 | elsif (defined( my $builder = $self->{'builder'})) { |
128 | if ($builder = $instance->can($builder)) { |
129 | $self->_set_initial_slot_value( |
130 | $meta_instance, |
131 | $instance, |
132 | $instance->$builder, |
133 | ); |
134 | } |
135 | else { |
136 | confess(ref($instance)." does not support builder method '". $self->{'builder'} ."' for attribute '" . $self->name . "'"); |
137 | } |
138 | } |
139 | } |
140 | |
141 | sub _set_initial_slot_value { |
142 | my ($self, $meta_instance, $instance, $value) = @_; |
143 | |
144 | my $slot_name = $self->name; |
145 | |
146 | return $meta_instance->set_slot_value($instance, $slot_name, $value) |
147 | unless $self->has_initializer; |
148 | |
149 | my $callback = $self->_make_initializer_writer_callback( |
150 | $meta_instance, $instance, $slot_name |
151 | ); |
152 | |
153 | my $initializer = $self->initializer; |
154 | |
155 | # most things will just want to set a value, so make it first arg |
156 | $instance->$initializer($value, $callback, $self); |
157 | } |
158 | |
159 | sub _make_initializer_writer_callback { |
160 | my $self = shift; |
161 | my ($meta_instance, $instance, $slot_name) = @_; |
162 | |
163 | return sub { |
164 | $meta_instance->set_slot_value($instance, $slot_name, $_[0]); |
165 | }; |
166 | } |
167 | |
168 | sub get_read_method { |
169 | my $self = shift; |
170 | my $reader = $self->reader || $self->accessor; |
171 | # normal case ... |
172 | return $reader unless ref $reader; |
173 | # the HASH ref case |
174 | my ($name) = %$reader; |
175 | return $name; |
176 | } |
177 | |
178 | sub get_write_method { |
179 | my $self = shift; |
180 | my $writer = $self->writer || $self->accessor; |
181 | # normal case ... |
182 | return $writer unless ref $writer; |
183 | # the HASH ref case |
184 | my ($name) = %$writer; |
185 | return $name; |
186 | } |
187 | |
188 | sub get_read_method_ref { |
189 | my $self = shift; |
190 | if ((my $reader = $self->get_read_method) && $self->associated_class) { |
191 | return $self->associated_class->get_method($reader); |
192 | } |
193 | else { |
194 | my $code = sub { $self->get_value(@_) }; |
195 | if (my $class = $self->associated_class) { |
196 | return $class->method_metaclass->wrap( |
197 | $code, |
198 | package_name => $class->name, |
199 | name => '__ANON__' |
200 | ); |
201 | } |
202 | else { |
203 | return $code; |
204 | } |
205 | } |
206 | } |
207 | |
208 | sub get_write_method_ref { |
209 | my $self = shift; |
210 | if ((my $writer = $self->get_write_method) && $self->associated_class) { |
211 | return $self->associated_class->get_method($writer); |
212 | } |
213 | else { |
214 | my $code = sub { $self->set_value(@_) }; |
215 | if (my $class = $self->associated_class) { |
216 | return $class->method_metaclass->wrap( |
217 | $code, |
218 | package_name => $class->name, |
219 | name => '__ANON__' |
220 | ); |
221 | } |
222 | else { |
223 | return $code; |
224 | } |
225 | } |
226 | } |
227 | |
228 | # slots |
229 | |
230 | sub slots { (shift)->name } |
231 | |
232 | # class association |
233 | |
234 | sub attach_to_class { |
235 | my ($self, $class) = @_; |
236 | (blessed($class) && $class->isa('Class::MOP::Class')) |
237 | || confess "You must pass a Class::MOP::Class instance (or a subclass)"; |
238 | weaken($self->{'associated_class'} = $class); |
239 | } |
240 | |
241 | sub detach_from_class { |
242 | my $self = shift; |
243 | $self->{'associated_class'} = undef; |
244 | } |
245 | |
246 | # method association |
247 | |
248 | sub associate_method { |
249 | my ($self, $method) = @_; |
250 | push @{$self->{'associated_methods'}} => $method; |
251 | } |
252 | |
253 | ## Slot management |
254 | |
255 | sub set_initial_value { |
256 | my ($self, $instance, $value) = @_; |
257 | $self->_set_initial_slot_value( |
258 | Class::MOP::Class->initialize(ref($instance))->get_meta_instance, |
259 | $instance, |
260 | $value |
261 | ); |
262 | } |
263 | |
264 | sub set_value { shift->set_raw_value(@_) } |
265 | |
266 | sub set_raw_value { |
267 | my $self = shift; |
268 | my ($instance, $value) = @_; |
269 | |
270 | my $mi = Class::MOP::Class->initialize(ref($instance))->get_meta_instance; |
271 | return $mi->set_slot_value($instance, $self->name, $value); |
272 | } |
273 | |
274 | sub _inline_set_value { |
275 | my $self = shift; |
276 | return $self->_inline_instance_set(@_) . ';'; |
277 | } |
278 | |
279 | sub _inline_instance_set { |
280 | my $self = shift; |
281 | my ($instance, $value) = @_; |
282 | |
283 | my $mi = $self->associated_class->get_meta_instance; |
284 | return $mi->inline_set_slot_value($instance, $self->name, $value); |
285 | } |
286 | |
287 | sub get_value { shift->get_raw_value(@_) } |
288 | |
289 | sub get_raw_value { |
290 | my $self = shift; |
291 | my ($instance) = @_; |
292 | |
293 | my $mi = Class::MOP::Class->initialize(ref($instance))->get_meta_instance; |
294 | return $mi->get_slot_value($instance, $self->name); |
295 | } |
296 | |
297 | sub _inline_get_value { |
298 | my $self = shift; |
299 | return $self->_inline_instance_get(@_) . ';'; |
300 | } |
301 | |
302 | sub _inline_instance_get { |
303 | my $self = shift; |
304 | my ($instance) = @_; |
305 | |
306 | my $mi = $self->associated_class->get_meta_instance; |
307 | return $mi->inline_get_slot_value($instance, $self->name); |
308 | } |
309 | |
310 | sub has_value { |
311 | my $self = shift; |
312 | my ($instance) = @_; |
313 | |
314 | my $mi = Class::MOP::Class->initialize(ref($instance))->get_meta_instance; |
315 | return $mi->is_slot_initialized($instance, $self->name); |
316 | } |
317 | |
318 | sub _inline_has_value { |
319 | my $self = shift; |
320 | return $self->_inline_instance_has(@_) . ';'; |
321 | } |
322 | |
323 | sub _inline_instance_has { |
324 | my $self = shift; |
325 | my ($instance) = @_; |
326 | |
327 | my $mi = $self->associated_class->get_meta_instance; |
328 | return $mi->inline_is_slot_initialized($instance, $self->name); |
329 | } |
330 | |
331 | sub clear_value { |
332 | my $self = shift; |
333 | my ($instance) = @_; |
334 | |
335 | my $mi = Class::MOP::Class->initialize(ref($instance))->get_meta_instance; |
336 | return $mi->deinitialize_slot($instance, $self->name); |
337 | } |
338 | |
339 | sub _inline_clear_value { |
340 | my $self = shift; |
341 | return $self->_inline_instance_clear(@_) . ';'; |
342 | } |
343 | |
344 | sub _inline_instance_clear { |
345 | my $self = shift; |
346 | my ($instance) = @_; |
347 | |
348 | my $mi = $self->associated_class->get_meta_instance; |
349 | return $mi->inline_deinitialize_slot($instance, $self->name); |
350 | } |
351 | |
352 | ## load em up ... |
353 | |
354 | sub accessor_metaclass { 'Class::MOP::Method::Accessor' } |
355 | |
356 | sub _process_accessors { |
357 | my ($self, $type, $accessor, $generate_as_inline_methods) = @_; |
358 | |
359 | my $method_ctx; |
360 | |
361 | if ( my $ctx = $self->definition_context ) { |
362 | $method_ctx = { %$ctx }; |
363 | } |
364 | |
365 | if (ref($accessor)) { |
366 | (ref($accessor) eq 'HASH') |
367 | || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref"; |
368 | my ($name, $method) = %{$accessor}; |
369 | $method = $self->accessor_metaclass->wrap( |
370 | $method, |
371 | package_name => $self->associated_class->name, |
372 | name => $name, |
373 | definition_context => $method_ctx, |
374 | ); |
375 | $self->associate_method($method); |
376 | return ($name, $method); |
377 | } |
378 | else { |
379 | my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable); |
380 | my $method; |
381 | try { |
382 | if ( $method_ctx ) { |
383 | my $desc = "accessor $accessor"; |
384 | if ( $accessor ne $self->name ) { |
385 | $desc .= " of attribute " . $self->name; |
386 | } |
387 | |
388 | $method_ctx->{description} = $desc; |
389 | } |
390 | |
391 | $method = $self->accessor_metaclass->new( |
392 | attribute => $self, |
393 | is_inline => $inline_me, |
394 | accessor_type => $type, |
395 | package_name => $self->associated_class->name, |
396 | name => $accessor, |
397 | definition_context => $method_ctx, |
398 | ); |
399 | } |
400 | catch { |
401 | confess "Could not create the '$type' method for " . $self->name . " because : $_"; |
402 | }; |
403 | $self->associate_method($method); |
404 | return ($accessor, $method); |
405 | } |
406 | } |
407 | |
408 | sub install_accessors { |
409 | my $self = shift; |
410 | my $inline = shift; |
411 | my $class = $self->associated_class; |
412 | |
413 | $class->add_method( |
414 | $self->_process_accessors('accessor' => $self->accessor(), $inline) |
415 | ) if $self->has_accessor(); |
416 | |
417 | $class->add_method( |
418 | $self->_process_accessors('reader' => $self->reader(), $inline) |
419 | ) if $self->has_reader(); |
420 | |
421 | $class->add_method( |
422 | $self->_process_accessors('writer' => $self->writer(), $inline) |
423 | ) if $self->has_writer(); |
424 | |
425 | $class->add_method( |
426 | $self->_process_accessors('predicate' => $self->predicate(), $inline) |
427 | ) if $self->has_predicate(); |
428 | |
429 | $class->add_method( |
430 | $self->_process_accessors('clearer' => $self->clearer(), $inline) |
431 | ) if $self->has_clearer(); |
432 | |
433 | return; |
434 | } |
435 | |
436 | { |
437 | my $_remove_accessor = sub { |
438 | my ($accessor, $class) = @_; |
439 | if (ref($accessor) && ref($accessor) eq 'HASH') { |
440 | ($accessor) = keys %{$accessor}; |
441 | } |
442 | my $method = $class->get_method($accessor); |
443 | $class->remove_method($accessor) |
444 | if (ref($method) && $method->isa('Class::MOP::Method::Accessor')); |
445 | }; |
446 | |
447 | sub remove_accessors { |
448 | my $self = shift; |
449 | # TODO: |
450 | # we really need to make sure to remove from the |
451 | # associates methods here as well. But this is |
452 | # such a slimly used method, I am not worried |
453 | # about it right now. |
454 | $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor(); |
455 | $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader(); |
456 | $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer(); |
457 | $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate(); |
458 | $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer(); |
459 | return; |
460 | } |
461 | |
462 | } |
463 | |
464 | 1; |
465 | |
466 | # ABSTRACT: Attribute Meta Object |
467 | |
468 | __END__ |
469 | |
470 | =pod |
471 | |
472 | =head1 SYNOPSIS |
473 | |
474 | Class::MOP::Attribute->new( |
475 | foo => ( |
476 | accessor => 'foo', # dual purpose get/set accessor |
477 | predicate => 'has_foo', # predicate check for defined-ness |
478 | init_arg => '-foo', # class->new will look for a -foo key |
479 | default => 'BAR IS BAZ!' # if no -foo key is provided, use this |
480 | ) |
481 | ); |
482 | |
483 | Class::MOP::Attribute->new( |
484 | bar => ( |
485 | reader => 'bar', # getter |
486 | writer => 'set_bar', # setter |
487 | predicate => 'has_bar', # predicate check for defined-ness |
488 | init_arg => ':bar', # class->new will look for a :bar key |
489 | # no default value means it is undef |
490 | ) |
491 | ); |
492 | |
493 | =head1 DESCRIPTION |
494 | |
495 | The Attribute Protocol is almost entirely an invention of |
496 | C<Class::MOP>. Perl 5 does not have a consistent notion of |
497 | attributes. There are so many ways in which this is done, and very few |
498 | (if any) are easily discoverable by this module. |
499 | |
500 | With that said, this module attempts to inject some order into this |
501 | chaos, by introducing a consistent API which can be used to create |
502 | object attributes. |
503 | |
504 | =head1 METHODS |
505 | |
506 | =head2 Creation |
507 | |
508 | =over 4 |
509 | |
510 | =item B<< Class::MOP::Attribute->new($name, ?%options) >> |
511 | |
512 | An attribute must (at the very least), have a C<$name>. All other |
513 | C<%options> are added as key-value pairs. |
514 | |
515 | =over 8 |
516 | |
517 | =item * init_arg |
518 | |
519 | This is a string value representing the expected key in an |
520 | initialization hash. For instance, if we have an C<init_arg> value of |
521 | C<-foo>, then the following code will Just Work. |
522 | |
523 | MyClass->meta->new_object( -foo => 'Hello There' ); |
524 | |
525 | If an init_arg is not assigned, it will automatically use the |
526 | attribute's name. If C<init_arg> is explicitly set to C<undef>, the |
527 | attribute cannot be specified during initialization. |
528 | |
529 | =item * builder |
530 | |
531 | This provides the name of a method that will be called to initialize |
532 | the attribute. This method will be called on the object after it is |
533 | constructed. It is expected to return a valid value for the attribute. |
534 | |
535 | =item * default |
536 | |
537 | This can be used to provide an explicit default for initializing the |
538 | attribute. If the default you provide is a subroutine reference, then |
539 | this reference will be called I<as a method> on the object. |
540 | |
541 | If the value is a simple scalar (string or number), then it can be |
542 | just passed as is. However, if you wish to initialize it with a HASH |
543 | or ARRAY ref, then you need to wrap that inside a subroutine |
544 | reference: |
545 | |
546 | Class::MOP::Attribute->new( |
547 | 'foo' => ( |
548 | default => sub { [] }, |
549 | ) |
550 | ); |
551 | |
552 | # or ... |
553 | |
554 | Class::MOP::Attribute->new( |
555 | 'foo' => ( |
556 | default => sub { {} }, |
557 | ) |
558 | ); |
559 | |
560 | If you wish to initialize an attribute with a subroutine reference |
561 | itself, then you need to wrap that in a subroutine as well: |
562 | |
563 | Class::MOP::Attribute->new( |
564 | 'foo' => ( |
565 | default => sub { |
566 | sub { print "Hello World" } |
567 | }, |
568 | ) |
569 | ); |
570 | |
571 | And lastly, if the value of your attribute is dependent upon some |
572 | other aspect of the instance structure, then you can take advantage of |
573 | the fact that when the C<default> value is called as a method: |
574 | |
575 | Class::MOP::Attribute->new( |
576 | 'object_identity' => ( |
577 | default => sub { Scalar::Util::refaddr( $_[0] ) }, |
578 | ) |
579 | ); |
580 | |
581 | Note that there is no guarantee that attributes are initialized in any |
582 | particular order, so you cannot rely on the value of some other |
583 | attribute when generating the default. |
584 | |
585 | =item * initializer |
586 | |
587 | This option can be either a method name or a subroutine |
588 | reference. This method will be called when setting the attribute's |
589 | value in the constructor. Unlike C<default> and C<builder>, the |
590 | initializer is only called when a value is provided to the |
591 | constructor. The initializer allows you to munge this value during |
592 | object construction. |
593 | |
594 | The initializer is called as a method with three arguments. The first |
595 | is the value that was passed to the constructor. The second is a |
596 | subroutine reference that can be called to actually set the |
597 | attribute's value, and the last is the associated |
598 | C<Class::MOP::Attribute> object. |
599 | |
600 | This contrived example shows an initializer that sets the attribute to |
601 | twice the given value. |
602 | |
603 | Class::MOP::Attribute->new( |
604 | 'doubled' => ( |
605 | initializer => sub { |
606 | my ( $self, $value, $set, $attr ) = @_; |
607 | $set->( $value * 2 ); |
608 | }, |
609 | ) |
610 | ); |
611 | |
612 | Since an initializer can be a method name, you can easily make |
613 | attribute initialization use the writer: |
614 | |
615 | Class::MOP::Attribute->new( |
616 | 'some_attr' => ( |
617 | writer => 'some_attr', |
618 | initializer => 'some_attr', |
619 | ) |
620 | ); |
621 | |
622 | Your writer will need to examine C<@_> and determine under which |
623 | context it is being called. |
624 | |
625 | =back |
626 | |
627 | The C<accessor>, C<reader>, C<writer>, C<predicate> and C<clearer> |
628 | options all accept the same parameters. You can provide the name of |
629 | the method, in which case an appropriate default method will be |
630 | generated for you. Or instead you can also provide hash reference |
631 | containing exactly one key (the method name) and one value. The value |
632 | should be a subroutine reference, which will be installed as the |
633 | method itself. |
634 | |
635 | =over 8 |
636 | |
637 | =item * accessor |
638 | |
639 | An C<accessor> is a standard Perl-style read/write accessor. It will |
640 | return the value of the attribute, and if a value is passed as an |
641 | argument, it will assign that value to the attribute. |
642 | |
643 | Note that C<undef> is a legitimate value, so this will work: |
644 | |
645 | $object->set_something(undef); |
646 | |
647 | =item * reader |
648 | |
649 | This is a basic read-only accessor. It returns the value of the |
650 | attribute. |
651 | |
652 | =item * writer |
653 | |
654 | This is a basic write accessor, it accepts a single argument, and |
655 | assigns that value to the attribute. |
656 | |
657 | Note that C<undef> is a legitimate value, so this will work: |
658 | |
659 | $object->set_something(undef); |
660 | |
661 | =item * predicate |
662 | |
663 | The predicate method returns a boolean indicating whether or not the |
664 | attribute has been explicitly set. |
665 | |
666 | Note that the predicate returns true even if the attribute was set to |
667 | a false value (C<0> or C<undef>). |
668 | |
669 | =item * clearer |
670 | |
671 | This method will uninitialize the attribute. After an attribute is |
672 | cleared, its C<predicate> will return false. |
673 | |
674 | =item * definition_context |
675 | |
676 | Mostly, this exists as a hook for the benefit of Moose. |
677 | |
678 | This option should be a hash reference containing several keys which |
679 | will be used when inlining the attribute's accessors. The keys should |
680 | include C<line>, the line number where the attribute was created, and |
681 | either C<file> or C<description>. |
682 | |
683 | This information will ultimately be used when eval'ing inlined |
684 | accessor code so that error messages report a useful line and file |
685 | name. |
686 | |
687 | =back |
688 | |
689 | =item B<< $attr->clone(%options) >> |
690 | |
691 | This clones the attribute. Any options you provide will override the |
692 | settings of the original attribute. You can change the name of the new |
693 | attribute by passing a C<name> key in C<%options>. |
694 | |
695 | =back |
696 | |
697 | =head2 Informational |
698 | |
699 | These are all basic read-only accessors for the values passed into |
700 | the constructor. |
701 | |
702 | =over 4 |
703 | |
704 | =item B<< $attr->name >> |
705 | |
706 | Returns the attribute's name. |
707 | |
708 | =item B<< $attr->accessor >> |
709 | |
710 | =item B<< $attr->reader >> |
711 | |
712 | =item B<< $attr->writer >> |
713 | |
714 | =item B<< $attr->predicate >> |
715 | |
716 | =item B<< $attr->clearer >> |
717 | |
718 | The C<accessor>, C<reader>, C<writer>, C<predicate>, and C<clearer> |
719 | methods all return exactly what was passed to the constructor, so it |
720 | can be either a string containing a method name, or a hash reference. |
721 | |
722 | =item B<< $attr->initializer >> |
723 | |
724 | Returns the initializer as passed to the constructor, so this may be |
725 | either a method name or a subroutine reference. |
726 | |
727 | =item B<< $attr->init_arg >> |
728 | |
729 | =item B<< $attr->is_default_a_coderef >> |
730 | |
731 | =item B<< $attr->default($instance) >> |
732 | |
733 | The C<$instance> argument is optional. If you don't pass it, the |
734 | return value for this method is exactly what was passed to the |
735 | constructor, either a simple scalar or a subroutine reference. |
736 | |
737 | If you I<do> pass an C<$instance> and the default is a subroutine |
738 | reference, then the reference is called as a method on the |
739 | C<$instance> and the generated value is returned. |
740 | |
741 | =item B<< $attr->slots >> |
742 | |
743 | Return a list of slots required by the attribute. This is usually just |
744 | one, the name of the attribute. |
745 | |
746 | A slot is the name of the hash key used to store the attribute in an |
747 | object instance. |
748 | |
749 | =item B<< $attr->get_read_method >> |
750 | |
751 | =item B<< $attr->get_write_method >> |
752 | |
753 | Returns the name of a method suitable for reading or writing the value |
754 | of the attribute in the associated class. |
755 | |
756 | If an attribute is read- or write-only, then these methods can return |
757 | C<undef> as appropriate. |
758 | |
759 | =item B<< $attr->has_read_method >> |
760 | |
761 | =item B<< $attr->has_write_method >> |
762 | |
763 | This returns a boolean indicating whether the attribute has a I<named> |
764 | read or write method. |
765 | |
766 | =item B<< $attr->get_read_method_ref >> |
767 | |
768 | =item B<< $attr->get_write_method_ref >> |
769 | |
770 | Returns the subroutine reference of a method suitable for reading or |
771 | writing the attribute's value in the associated class. These methods |
772 | always return a subroutine reference, regardless of whether or not the |
773 | attribute is read- or write-only. |
774 | |
775 | =item B<< $attr->insertion_order >> |
776 | |
777 | If this attribute has been inserted into a class, this returns a zero |
778 | based index regarding the order of insertion. |
779 | |
780 | =back |
781 | |
782 | =head2 Informational predicates |
783 | |
784 | These are all basic predicate methods for the values passed into C<new>. |
785 | |
786 | =over 4 |
787 | |
788 | =item B<< $attr->has_accessor >> |
789 | |
790 | =item B<< $attr->has_reader >> |
791 | |
792 | =item B<< $attr->has_writer >> |
793 | |
794 | =item B<< $attr->has_predicate >> |
795 | |
796 | =item B<< $attr->has_clearer >> |
797 | |
798 | =item B<< $attr->has_initializer >> |
799 | |
800 | =item B<< $attr->has_init_arg >> |
801 | |
802 | This will be I<false> if the C<init_arg> was set to C<undef>. |
803 | |
804 | =item B<< $attr->has_default >> |
805 | |
806 | This will be I<false> if the C<default> was set to C<undef>, since |
807 | C<undef> is the default C<default> anyway. |
808 | |
809 | =item B<< $attr->has_builder >> |
810 | |
811 | =item B<< $attr->has_insertion_order >> |
812 | |
813 | This will be I<false> if this attribute has not be inserted into a class |
814 | |
815 | =back |
816 | |
817 | =head2 Value management |
818 | |
819 | These methods are basically "back doors" to the instance, and can be |
820 | used to bypass the regular accessors, but still stay within the MOP. |
821 | |
822 | These methods are not for general use, and should only be used if you |
823 | really know what you are doing. |
824 | |
825 | =over 4 |
826 | |
827 | =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >> |
828 | |
829 | This method is used internally to initialize the attribute's slot in |
830 | the object C<$instance>. |
831 | |
832 | The C<$params> is a hash reference of the values passed to the object |
833 | constructor. |
834 | |
835 | It's unlikely that you'll need to call this method yourself. |
836 | |
837 | =item B<< $attr->set_value($instance, $value) >> |
838 | |
839 | Sets the value without going through the accessor. Note that this |
840 | works even with read-only attributes. |
841 | |
842 | =item B<< $attr->set_raw_value($instance, $value) >> |
843 | |
844 | Sets the value with no side effects such as a trigger. |
845 | |
846 | This doesn't actually apply to Class::MOP attributes, only to subclasses. |
847 | |
848 | =item B<< $attr->set_initial_value($instance, $value) >> |
849 | |
850 | Sets the value without going through the accessor. This method is only |
851 | called when the instance is first being initialized. |
852 | |
853 | =item B<< $attr->get_value($instance) >> |
854 | |
855 | Returns the value without going through the accessor. Note that this |
856 | works even with write-only accessors. |
857 | |
858 | =item B<< $attr->get_raw_value($instance) >> |
859 | |
860 | Returns the value without any side effects such as lazy attributes. |
861 | |
862 | Doesn't actually apply to Class::MOP attributes, only to subclasses. |
863 | |
864 | =item B<< $attr->has_value($instance) >> |
865 | |
866 | Return a boolean indicating whether the attribute has been set in |
867 | C<$instance>. This how the default C<predicate> method works. |
868 | |
869 | =item B<< $attr->clear_value($instance) >> |
870 | |
871 | This will clear the attribute's value in C<$instance>. This is what |
872 | the default C<clearer> calls. |
873 | |
874 | Note that this works even if the attribute does not have any |
875 | associated read, write or clear methods. |
876 | |
877 | =back |
878 | |
879 | =head2 Class association |
880 | |
881 | These methods allow you to manage the attributes association with |
882 | the class that contains it. These methods should not be used |
883 | lightly, nor are they very magical, they are mostly used internally |
884 | and by metaclass instances. |
885 | |
886 | =over 4 |
887 | |
888 | =item B<< $attr->associated_class >> |
889 | |
890 | This returns the C<Class::MOP::Class> with which this attribute is |
891 | associated, if any. |
892 | |
893 | =item B<< $attr->attach_to_class($metaclass) >> |
894 | |
895 | This method stores a weakened reference to the C<$metaclass> object |
896 | internally. |
897 | |
898 | This method does not remove the attribute from its old class, |
899 | nor does it create any accessors in the new class. |
900 | |
901 | It is probably best to use the L<Class::MOP::Class> C<add_attribute> |
902 | method instead. |
903 | |
904 | =item B<< $attr->detach_from_class >> |
905 | |
906 | This method removes the associate metaclass object from the attribute |
907 | it has one. |
908 | |
909 | This method does not remove the attribute itself from the class, or |
910 | remove its accessors. |
911 | |
912 | It is probably best to use the L<Class::MOP::Class> |
913 | C<remove_attribute> method instead. |
914 | |
915 | =back |
916 | |
917 | =head2 Attribute Accessor generation |
918 | |
919 | =over 4 |
920 | |
921 | =item B<< $attr->accessor_metaclass >> |
922 | |
923 | Accessor methods are generated using an accessor metaclass. By |
924 | default, this is L<Class::MOP::Method::Accessor>. This method returns |
925 | the name of the accessor metaclass that this attribute uses. |
926 | |
927 | =item B<< $attr->associate_method($method) >> |
928 | |
929 | This associates a L<Class::MOP::Method> object with the |
930 | attribute. Typically, this is called internally when an attribute |
931 | generates its accessors. |
932 | |
933 | =item B<< $attr->associated_methods >> |
934 | |
935 | This returns the list of methods which have been associated with the |
936 | attribute. |
937 | |
938 | =item B<< $attr->install_accessors >> |
939 | |
940 | This method generates and installs code the attributes various |
941 | accessors. It is typically called from the L<Class::MOP::Class> |
942 | C<add_attribute> method. |
943 | |
944 | =item B<< $attr->remove_accessors >> |
945 | |
946 | This method removes all of the accessors associated with the |
947 | attribute. |
948 | |
949 | This does not currently remove methods from the list returned by |
950 | C<associated_methods>. |
951 | |
952 | =item B<< $attr->inline_get >> |
953 | |
954 | =item B<< $attr->inline_set >> |
955 | |
956 | =item B<< $attr->inline_has >> |
957 | |
958 | =item B<< $attr->inline_clear >> |
959 | |
960 | These methods return a code snippet suitable for inlining the relevant |
961 | operation. They expect strings containing variable names to be used in the |
962 | inlining, like C<'$self'> or C<'$_[1]'>. |
963 | |
964 | =back |
965 | |
966 | =head2 Introspection |
967 | |
968 | =over 4 |
969 | |
970 | =item B<< Class::MOP::Attribute->meta >> |
971 | |
972 | This will return a L<Class::MOP::Class> instance for this class. |
973 | |
974 | It should also be noted that L<Class::MOP> will actually bootstrap |
975 | this module by installing a number of attribute meta-objects into its |
976 | metaclass. |
977 | |
978 | =back |
979 | |
980 | =cut |
981 | |
982 | |