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.\" ========================================================================
.\"
.IX Title "Class::Meta::Attribute 3pm"
.TH Class::Meta::Attribute 3pm "2022-06-11" "perl v5.34.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Class::Meta::Attribute \- Class::Meta class attribute introspection
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 3
\&  # Assuming MyApp::Thingy was generated by Class::Meta.
\&  my $class = MyApp::Thingy\->my_class;
\&  my $thingy = MyApp::Thingy\->new;
\&
\&  print "\enAttributes:\en";
\&  for my $attr ($class\->attributes) {
\&      print "  o ", $attr\->name, " => ", $attr\->get($thingy), $/;
\&      if ($attr\->authz >= Class::Meta::SET && $attr\->type eq \*(Aqstring\*(Aq) {
\&          $attr\->get($thingy, \*(Aqhey there!\*(Aq);
\&          print "    Changed to: ", $attr\->get($thingy) $/;
\&      }
\&  }
.Ve
.SH "DESCRIPTION"
.IX Header "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.
.PP
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 \f(CW\*(C`my_class()\*(C'\fR method to retrieve
its Class::Meta::Class object, and then call the \f(CW\*(C`attributes()\*(C'\fR method on the
Class::Meta::Class object.
.SH "INTERFACE"
.IX Header "INTERFACE"
.SS "Constructors"
.IX Subsection "Constructors"
\fInew\fR
.IX Subsection "new"
.PP
A protected method for constructing a Class::Meta::Attribute object. Do not
call this method directly; Call the
\&\f(CW\*(C`add_attribute()\*(C'\fR method on a Class::Meta
object, instead.
.SS "Instance Methods"
.IX Subsection "Instance Methods"
\fIname\fR
.IX Subsection "name"
.PP
.Vb 1
\&  my $name = $attr\->name;
.Ve
.PP
Returns the name of the attribute.
.PP
\fItype\fR
.IX Subsection "type"
.PP
.Vb 1
\&  my $type = $attr\->type;
.Ve
.PP
Returns the name of the attribute's data type. Typical values are \*(L"scalar\*(R",
\&\*(L"string\*(R", and \*(L"boolean\*(R". See Class::Meta for a
complete list.
.PP
\fIis\fR
.IX Subsection "is"
.PP
.Vb 3
\&  if ($attr\->is(\*(Aqstring\*(Aq)) {
\&      # ...
\&  }
.Ve
.PP
A convenience method for \f(CW\*(C`$attr\->type eq $type\*(C'\fR.
.PP
\fIdesc\fR
.IX Subsection "desc"
.PP
.Vb 1
\&  my $desc = $attr\->desc;
.Ve
.PP
Returns a description of the attribute.
.PP
\fIlabel\fR
.IX Subsection "label"
.PP
.Vb 1
\&  my $label = $attr\->label;
.Ve
.PP
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.
.PP
\fIrequired\fR
.IX Subsection "required"
.PP
.Vb 1
\&  my $req = $attr\->required;
.Ve
.PP
Indicates if the attribute is required to have a value.
.PP
\fIonce\fR
.IX Subsection "once"
.PP
.Vb 1
\&  my $once = $attr\->once;
.Ve
.PP
Indicates whether an attribute value can be set to a defined value only once.
.PP
\fIpackage\fR
.IX Subsection "package"
.PP
.Vb 1
\&  my $package = $attr\->package;
.Ve
.PP
Returns the package name of the class that attribute is associated with.
.PP
\fIview\fR
.IX Subsection "view"
.PP
.Vb 1
\&  my $view = $attr\->view;
.Ve
.PP
Returns the view of the attribute, reflecting its visibility. The possible
values are defined by the following constants:
.IP "Class::Meta::PUBLIC" 4
.IX Item "Class::Meta::PUBLIC"
.PD 0
.IP "Class::Meta::PRIVATE" 4
.IX Item "Class::Meta::PRIVATE"
.IP "Class::Meta::TRUSTED" 4
.IX Item "Class::Meta::TRUSTED"
.IP "Class::Meta::PROTECTED" 4
.IX Item "Class::Meta::PROTECTED"
.PD
.PP
\fIcontext\fR
.IX Subsection "context"
.PP
.Vb 1
\&  my $context = $attr\->context;
.Ve
.PP
Returns the context of the attribute, essentially whether it is a class or
object attribute. The possible values are defined by the following constants:
.IP "Class::Meta::CLASS" 4
.IX Item "Class::Meta::CLASS"
.PD 0
.IP "Class::Meta::OBJECT" 4
.IX Item "Class::Meta::OBJECT"
.PD
.PP
\fIauthz\fR
.IX Subsection "authz"
.PP
.Vb 1
\&  my $authz = $attr\->authz;
.Ve
.PP
Returns the authorization for the attribute, which determines whether it can be
read or changed. The possible values are defined by the following constants:
.IP "Class::Meta::READ" 4
.IX Item "Class::Meta::READ"
.PD 0
.IP "Class::Meta::WRITE" 4
.IX Item "Class::Meta::WRITE"
.IP "Class::Meta::RDWR" 4
.IX Item "Class::Meta::RDWR"
.IP "Class::Meta::NONE" 4
.IX Item "Class::Meta::NONE"
.PD
.PP
\fIclass\fR
.IX Subsection "class"
.PP
.Vb 1
\&  my $class = $attr\->class;
.Ve
.PP
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 \fInot\fR any of its subclasses.
.PP
\fIdefault\fR
.IX Subsection "default"
.PP
.Vb 1
\&  my $default = $attr\->default;
.Ve
.PP
Returns the default value for a new instance of this attribute. Since the
default value can be determined dynamically, the value returned by
\&\f(CW\*(C`default()\*(C'\fR may change on subsequent calls. It all depends on what was
passed for the \f(CW\*(C`default\*(C'\fR parameter in the call to \f(CW\*(C`add_attribute()\*(C'\fR on the
Class::Meta object that generated the class.
.PP
\fIget\fR
.IX Subsection "get"
.PP
.Vb 1
\&  my $value = $attr\->get($thingy);
.Ve
.PP
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 \f(CW\*(C`goto\*(C'\fR to execute the accessor, so the call to \f(CW\*(C`set()\*(C'\fR itself
will not appear in a call stack trace.
.PP
\fIset\fR
.IX Subsection "set"
.PP
.Vb 1
\&  $attr\->set($thingy, $new_value);
.Ve
.PP
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 \f(CW\*(C`goto\*(C'\fR to execute the
accessor, so the call to \f(CW\*(C`set()\*(C'\fR itself will not appear in a call stack
trace.
.PP
\fIbuild\fR
.IX Subsection "build"
.PP
.Vb 1
\&  $attr\->build($class);
.Ve
.PP
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 \f(CW\*(C`make_attr_get()\*(C'\fR and
\&\f(CW\*(C`make_attr_set()\*(C'\fR methods of Class::Meta::Type as appropriate for the
Class::Meta::Attribute object.
.PP
Although you should never call this method directly, subclasses of
Class::Meta::Constructor may need to override its behavior.
.SH "SUPPORT"
.IX Header "SUPPORT"
This module is stored in an open GitHub
repository <http://github.com/theory/class-meta/>. Feel free to fork and
contribute!
.PP
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>.
.SH "AUTHOR"
.IX Header "AUTHOR"
David E. Wheeler <david@justatheory.com>
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Other classes of interest within the Class::Meta distribution include:
.IP "Class::Meta" 4
.IX Item "Class::Meta"
.PD 0
.IP "Class::Meta::Class" 4
.IX Item "Class::Meta::Class"
.IP "Class::Meta::Method" 4
.IX Item "Class::Meta::Method"
.IP "Class::Meta::Constructor" 4
.IX Item "Class::Meta::Constructor"
.IP "Class::Meta::Type" 4
.IX Item "Class::Meta::Type"
.PD
.SH "COPYRIGHT AND LICENSE"
.IX Header "COPYRIGHT AND LICENSE"
Copyright (c) 2002\-2011, David E. Wheeler. Some Rights Reserved.
.PP
This module is free software; you can redistribute it and/or modify it under
the same terms as Perl itself.