--- name: "Class::Meta::Attribute" section: "3pm" platform: "linux" package: "libclass-meta-perl" version: "0.66-3" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/Class::Meta::Attribute" --- # Class::Meta::Attribute(3pm) Class::Meta class attribute introspection ## NAME Class::Meta::Attribute - Class::Meta class attribute introspection ## SYNOPSIS ``` # Assuming MyApp::Thingy was generated by Class::Meta. my $class = MyApp::Thingy->my_class; my $thingy = MyApp::Thingy->new; print "\nAttributes:\n"; for my $attr ($class->attributes) { print " o ", $attr->name, " => ", $attr->get($thingy), $/; if ($attr->authz >= Class::Meta::SET && $attr->type eq 'string') { $attr->get($thingy, 'hey there!'); print " Changed to: ", $attr->get($thingy) $/; } } ``` ## DESCRIPTION An object of this class describes an attribute of a class created by Class::Meta. It includes meta data such as the name of the attribute, its data type, its accessibility, and whether or not a value is required. It also provides methods to easily get and set the value of the attribute for a given instance of the class. Class::Meta::Attribute objects are created by Class::Meta; they are never instantiated directly in client code. To access the attribute objects for a Class::Meta-generated class, simply call its `"my_class()"` method to retrieve its Class::Meta::Class object, and then call the `"attributes()"` method on the Class::Meta::Class object. ## INTERFACE ### Constructors *new* A protected method for constructing a Class::Meta::Attribute object. Do not call this method directly; Call the `"add_attribute()"` method on a Class::Meta object, instead. ### Instance Methods *name* ``` my $name = $attr->name; ``` Returns the name of the attribute. *type* ``` my $type = $attr->type; ``` Returns the name of the attribute's data type. Typical values are "scalar", "string", and "boolean". See Class::Meta for a complete list. *is* ``` if ($attr->is('string')) { # ... } ``` A convenience method for `"$attr->type eq $type"`. *desc* ``` my $desc = $attr->desc; ``` Returns a description of the attribute. *label* ``` my $label = $attr->label; ``` Returns a label for the attribute, suitable for use in a user interface. It is distinguished from the attribute name, which functions to name the accessor methods for the attribute. *required* ``` my $req = $attr->required; ``` Indicates if the attribute is required to have a value. *once* ``` my $once = $attr->once; ``` Indicates whether an attribute value can be set to a defined value only once. *package* ``` my $package = $attr->package; ``` Returns the package name of the class that attribute is associated with. *view* ``` my $view = $attr->view; ``` Returns the view of the attribute, reflecting its visibility. The possible values are defined by the following constants: - Class::Meta::PUBLIC - Class::Meta::PRIVATE - Class::Meta::TRUSTED - Class::Meta::PROTECTED *context* ``` my $context = $attr->context; ``` Returns the context of the attribute, essentially whether it is a class or object attribute. The possible values are defined by the following constants: - Class::Meta::CLASS - Class::Meta::OBJECT *authz* ``` my $authz = $attr->authz; ``` Returns the authorization for the attribute, which determines whether it can be read or changed. The possible values are defined by the following constants: - Class::Meta::READ - Class::Meta::WRITE - Class::Meta::RDWR - Class::Meta::NONE *class* ``` my $class = $attr->class; ``` Returns the Class::Meta::Class object that this attribute is associated with. Note that this object will always represent the class in which the attribute is defined, and *not* any of its subclasses. *default* ``` my $default = $attr->default; ``` Returns the default value for a new instance of this attribute. Since the default value can be determined dynamically, the value returned by `"default()"` may change on subsequent calls. It all depends on what was passed for the `"default"` parameter in the call to `"add_attribute()"` on the Class::Meta object that generated the class. *get* ``` my $value = $attr->get($thingy); ``` This method calls the "get" accessor method on the object passed as the sole argument and returns the value of the attribute for that object. Note that it uses a `"goto"` to execute the accessor, so the call to `"set()"` itself will not appear in a call stack trace. *set* ``` $attr->set($thingy, $new_value); ``` This method calls the "set" accessor method on the object passed as the first argument and passes any remaining arguments to assign a new value to the attribute for that object. Note that it uses a `"goto"` to execute the accessor, so the call to `"set()"` itself will not appear in a call stack trace. *build* ``` $attr->build($class); ``` This is a protected method, designed to be called only by the Class::Meta class or a subclass of Class::Meta. It takes a single argument, the Class::Meta::Class object for the class in which the attribute was defined, and generates attribute accessors by calling out to the `"make_attr_get()"` and `"make_attr_set()"` methods of Class::Meta::Type as appropriate for the Class::Meta::Attribute object. Although you should never call this method directly, subclasses of Class::Meta::Constructor may need to override its behavior. ## SUPPORT This module is stored in an open GitHub repository \. Feel free to fork and contribute! Please file bug reports via GitHub Issues \ or by sending mail to bug-Class-Meta@rt.cpan.org \. ## AUTHOR David E. Wheeler \ ## SEE ALSO Other classes of interest within the Class::Meta distribution include: - Class::Meta - Class::Meta::Class - Class::Meta::Method - Class::Meta::Constructor - Class::Meta::Type ## COPYRIGHT AND LICENSE Copyright (c) 2002-2011, David E. Wheeler. Some Rights Reserved. This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.