Class::Meta::Attribute - Class::Meta class attribute introspection

       David E. Wheeler <david@justatheory.com>

       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.

perl v5.40.1                                       2025-02-18                        Class::Meta::Attribute(3pm)

       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.

Constructorsnew

       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.

   InstanceMethodsname

         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.

       Class::Meta::Attribute - Class::Meta class attribute introspection

       Other classes of interest within the Class::Meta distribution include:

       Class::Meta
       Class::Meta::Class
       Class::Meta::Method
       Class::Meta::Constructor
       Class::Meta::Type

       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 bug-Class-Meta@rt.cpan.org <mailto:bug-Class-Meta@rt.cpan.org>.

         # 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) $/;
             }
         }