1Moose::Meta::Attribute(U3s)er Contributed Perl DocumentatMiooonse::Meta::Attribute(3)
2
6 Moose::Meta::Attribute - The Moose attribute metaclass
7
9 This is a subclass of Class::MOP::Attribute with Moose specific exten‐
10 sions.
11 For the most part, the only time you will ever encounter an instance of
13 this class is if you are doing some serious deep introspection. To
14 really understand this class, you need to refer to the
15 Class::MOP::Attribute documentation.
16
18 Overridden methods
19 These methods override methods in Class::MOP::Attribute and add Moose
21 specific features. You can safely assume though that they will behave
22 just as Class::MOP::Attribute does.
23 new
25 initialize_instance_slot
26 install_accessors
27 accessor_metaclass
28 get_value
29 set_value
30 eval { $point->meta->get_attribute('x')->set_value($point, 'fourty-two') };
31 if($@) {
32 print "Oops: $@\n";
33 }
34 Attribute (x) does not pass the type constraint (Int) with
36 'fourty-two'
37 Before setting the value, a check is made on the type constraint of
39 the attribute, if it has one, to see if the value passes it. If the
40 value fails to pass, the set operation dies with a "confess" in
41 Carp.
42 Any coercion to convert values is done before checking the type
44 constraint.
45 To check a value against a type constraint before setting it, fetch
47 the attribute instance using "find_attribute_by_name" in
48 Moose::Meta::Attribute, fetch the type_constraint from the
49 attribute using "type_constraint" in Moose::Meta::Attribute and
50 call "check" in Moose::Meta::TypeConstraint. See Moose::Cook‐
51 book::RecipeX for an example.
52 Additional Moose features
54 Moose attributes support type-constraint checking, weak reference cre‐
56 ation and type coercion.
57 clone_and_inherit_options
59 This is to support the "has '+foo'" feature, it clones an attribute
60 from a superclass and allows a very specific set of changes to be
61 made to the attribute.
62 has_type_constraint
64 Returns true if this meta-attribute has a type constraint.
65 type_constraint
67 A read-only accessor for this meta-attribute's type constraint. For
68 more information on what you can do with this, see the documenta‐
69 tion for Moose::Meta::TypeConstraint.
70 has_handles
72 Returns true if this meta-attribute performs delegation.
73 handles
75 This returns the value which was passed into the handles option.
76 is_weak_ref
78 Returns true if this meta-attribute produces a weak reference.
79 is_required
81 Returns true if this meta-attribute is required to have a value.
82 is_lazy
84 Returns true if this meta-attribute should be initialized lazily.
85 NOTE: lazy attributes, must have a "default" or "builder" field
87 set.
88 is_lazy_build
90 Returns true if this meta-attribute should be initialized lazily
91 through the builder generated by lazy_build. Using "lazy_build =>
92 1" will make your attribute required and lazy. In addition it will
93 set the builder, clearer and predicate options for you using the
94 following convention.
95 #If your attribute name starts with an underscore:
97 has '_foo' => (lazy_build => 1);
98 #is the same as
99 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', builder => '_build__foo);
100 # or
101 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', default => sub{shift->_build__foo});
102 #If your attribute name does not start with an underscore:
104 has 'foo' => (lazy_build => 1);
105 #is the same as
106 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', builder => '_build_foo);
107 # or
108 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', default => sub{shift->_build_foo});
109 The reason for the different naming of the "builder" is that the
111 "builder" method is a private method while the "clearer" and "pred‐
112 icate" methods are public methods.
113 NOTE: This means your class should provide a method whose name
115 matches the value of the builder part, in this case _build__foo or
116 _build_foo.
117 should_coerce
119 Returns true if this meta-attribute should perform type coercion.
120 should_auto_deref
122 Returns true if this meta-attribute should perform automatic
123 auto-dereferencing.
124 NOTE: This can only be done for attributes whose type constraint is
126 either ArrayRef or HashRef.
127 has_trigger
129 Returns true if this meta-attribute has a trigger set.
130 trigger
132 This is a CODE reference which will be executed every time the
133 value of an attribute is assigned. The CODE ref will get two val‐
134 ues, the invocant and the new value. This can be used to handle
135 basic bi-directional relations.
136 documentation
138 This is a string which contains the documentation for this
139 attribute. It serves no direct purpose right now, but it might in
140 the future in some kind of automated documentation system perhaps.
141 has_documentation
143 Returns true if this meta-attribute has any documentation.
144
146 All complex software has bugs lurking in it, and this module is no
147 exception. If you find a bug please either email me, or add the bug to
148 cpan-RT.
149
151 Stevan Little <stevan@iinteractive.com>
152 Yuval Kogman <nothingmuch@woobling.com>
154
156 Copyright 2006, 2007 by Infinity Interactive, Inc.
157 <http://www.iinteractive.com>
159 This library is free software; you can redistribute it and/or modify it
161 under the same terms as Perl itself.
162perl v5.8.8 2007-09-06 Moose::Meta::Attribute(3)