Class::meta class attribute introspection
# 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) $/;
}
}
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 \*(C`my_class()\*(C' method to retrieve its Class::Meta::Class object, and then call the \*(C`attributes()\*(C' method on the Class::Meta::Class object.
new
A protected method for constructing a Class::Meta::Attribute object. Do not call this method directly; Call the \*(C`add_attribute()\*(C' method on a Class::Meta object, instead.
name
my $name = $attr->name;
Returns the name of the attribute.
type
my $type = $attr->type;
Returns the name of the attribute's data type. Typical values are \*(L"scalar\*(R", \*(L"string\*(R", and \*(L"boolean\*(R". See Class::Meta for a complete list.
is
if ($attr->is('string')) { # ... }
A convenience method for \*(C`$attr->type eq $type\*(C'.
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:
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:
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
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 \*(C`default()\*(C' may change on subsequent calls. It all depends on what was passed for the \*(C`default\*(C' parameter in the call to \*(C`add_attribute()\*(C' on the Class::Meta object that generated the class.
get
my $value = $attr->get($thingy);
This method calls the \*(L"get\*(R" 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 \*(C`goto\*(C' to execute the accessor, so the call to \*(C`set()\*(C' itself will not appear in a call stack trace.
set
$attr->set($thingy, $new_value);
This method calls the \*(L"set\*(R" 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 \*(C`goto\*(C' to execute the accessor, so the call to \*(C`set()\*(C' 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 \*(C`make_attr_get()\*(C' and \*(C`make_attr_set()\*(C' 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.
This module is stored in an open GitHub repository <http://github.com/theory/class-meta/>. Feel free to fork and contribute!
Please file bug reports via GitHub Issues <http://github.com/theory/class-meta/issues/> or by sending mail to [email protected] <mailto:[email protected]>.
David E. Wheeler <[email protected]>
Other classes of interest within the Class::Meta distribution include:
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.