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Moose::Meta::Attribute(3)            User Contributed Perl Documentation           Moose::Meta::Attribute(3)



NAME
       Moose::Meta::Attribute - The Moose attribute metaclass

VERSION
       version 2.0604

DESCRIPTION
       This class is a subclass of Class::MOP::Attribute that provides additional Moose-specific
       functionality.

       To really understand this class, you will need to start with the Class::MOP::Attribute documentation.
       This class can be understood as a set of additional features on top of the basic feature provided by
       that parent class.

INHERITANCE
       "Moose::Meta::Attribute" is a subclass of Class::MOP::Attribute.

METHODS
       Many of the documented below override methods in Class::MOP::Attribute and add Moose specific
       features.

   Creation
       Moose::Meta::Attribute->new(%options)
           This method overrides the Class::MOP::Attribute constructor.

           Many of the options below are described in more detail in the Moose::Manual::Attributes document.

           It adds the following options to the constructor:

           •       is => 'ro', 'rw', 'bare'

                   This provides a shorthand for specifying the "reader", "writer", or "accessor" names. If
                   the attribute is read-only ('ro') then it will have a "reader" method with the same
                   attribute as the name.

                   If it is read-write ('rw') then it will have an "accessor" method with the same name. If
                   you provide an explicit "writer" for a read-write attribute, then you will have a
                   "reader" with the same name as the attribute, and a "writer" with the name you provided.

                   Use 'bare' when you are deliberately not installing any methods (accessor, reader, etc.)
                   associated with this attribute; otherwise, Moose will issue a deprecation warning when
                   this attribute is added to a metaclass.

           •       isa => $type

                   This option accepts a type. The type can be a string, which should be a type name. If the
                   type name is unknown, it is assumed to be a class name.

                   This option can also accept a Moose::Meta::TypeConstraint object.

                   If you also provide a "does" option, then your "isa" option must be a class name, and
                   that class must do the role specified with "does".

           •       does => $role

                   This is short-hand for saying that the attribute's type must be an object which does the
                   named role.

           •       coerce => $bool

                   This option is only valid for objects with a type constraint ("isa") that defined a
                   coercion. If this is true, then coercions will be applied whenever this attribute is set.

                   You can make both this and the "weak_ref" option true.

           •       trigger => $sub

                   This option accepts a subroutine reference, which will be called after the attribute is
                   set.

           •       required => $bool

                   An attribute which is required must be provided to the constructor. An attribute which is
                   required can also have a "default" or "builder", which will satisfy its required-ness.

                   A required attribute must have a "default", "builder" or a non-"undef" "init_arg"

           •       lazy => $bool

                   A lazy attribute must have a "default" or "builder". When an attribute is lazy, the
                   default value will not be calculated until the attribute is read.

           •       weak_ref => $bool

                   If this is true, the attribute's value will be stored as a weak reference.

           •       auto_deref => $bool

                   If this is true, then the reader will dereference the value when it is called. The
                   attribute must have a type constraint which defines the attribute as an array or hash
                   reference.

           •       lazy_build => $bool

                   Setting this to true makes the attribute lazy and provides a number of default methods.

                     has 'size' => (
                         is         => 'ro',
                         lazy_build => 1,
                     );

                   is equivalent to this:

                     has 'size' => (
                         is        => 'ro',
                         lazy      => 1,
                         builder   => '_build_size',
                         clearer   => 'clear_size',
                         predicate => 'has_size',
                     );

                   If your attribute name starts with an underscore ("_"), then the clearer and predicate
                   will as well:

                     has '_size' => (
                         is         => 'ro',
                         lazy_build => 1,
                     );

                   becomes:

                     has '_size' => (
                         is        => 'ro',
                         lazy      => 1,
                         builder   => '_build__size',
                         clearer   => '_clear_size',
                         predicate => '_has_size',
                     );

                   Note the doubled underscore in the builder name. Internally, Moose simply prepends the
                   attribute name with "_build_" to come up with the builder name.

           •       documentation

                   An arbitrary string that can be retrieved later by calling "$attr->documentation".

       $attr->clone(%options)
           This creates a new attribute based on attribute being cloned. You must supply a "name" option to
           provide a new name for the attribute.

           The %options can only specify options handled by Class::MOP::Attribute.

   Value management
       $attr->initialize_instance_slot($meta_instance, $instance, $params)
           This method is used internally to initialize the attribute's slot in the object $instance.

           This overrides the Class::MOP::Attribute method to handle lazy attributes, weak references, and
           type constraints.

       get_value
       set_value
             eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
             if($@) {
               print "Oops: $@\n";
             }

           Attribute (x) does not pass the type constraint (Int) with 'forty-two'

           Before setting the value, a check is made on the type constraint of the attribute, if it has one,
           to see if the value passes it. If the value fails to pass, the set operation dies.

           Any coercion to convert values is done before checking the type constraint.

           To check a value against a type constraint before setting it, fetch the attribute instance using
           "find_attribute_by_name" in Class::MOP::Class, fetch the type_constraint from the attribute using
           "type_constraint" in Moose::Meta::Attribute and call "check" in Moose::Meta::TypeConstraint. See
           Moose::Cookbook::Basics::Company_Subtypes for an example.

   Attribute Accessor generation
       $attr->install_accessors
           This method overrides the parent to also install delegation methods.

           If, after installing all methods, the attribute object has no associated methods, it throws an
           error unless "is => 'bare'" was passed to the attribute constructor.  (Trying to add an attribute
           that has no associated methods is almost always an error.)

       $attr->remove_accessors
           This method overrides the parent to also remove delegation methods.

       $attr->inline_set($instance_var, $value_var)
           This method return a code snippet suitable for inlining the relevant operation. It expect strings
           containing variable names to be used in the inlining, like '$self' or '$_[1]'.

       $attr->install_delegation
           This method adds its delegation methods to the attribute's associated class, if it has any to
           add.

       $attr->remove_delegation
           This method remove its delegation methods from the attribute's associated class.

       $attr->accessor_metaclass
           Returns the accessor metaclass name, which defaults to Moose::Meta::Method::Accessor.

       $attr->delegation_metaclass
           Returns the delegation metaclass name, which defaults to Moose::Meta::Method::Delegation.

   Additional Moose features
       These methods are not found in the superclass. They support features provided by Moose.

       $attr->does($role)
           This indicates whether the attribute itself does the given role. The role can be given as a full
           class name, or as a resolvable trait name.

           Note that this checks the attribute itself, not its type constraint, so it is checking the
           attribute's metaclass and any traits applied to the attribute.

       Moose::Meta::Class->interpolate_class_and_new($name, %options)
           This is an alternate constructor that handles the "metaclass" and "traits" options.

           Effectively, this method is a factory that finds or creates the appropriate class for the given
           "metaclass" and/or "traits".

           Once it has the appropriate class, it will call "$class->new($name, %options)" on that class.

       $attr->clone_and_inherit_options(%options)
           This method supports the "has '+foo'" feature. It does various bits of processing on the supplied
           %options before ultimately calling the "clone" method.

           One of its main tasks is to make sure that the %options provided does not include the options
           returned by the "illegal_options_for_inheritance" method.

       $attr->illegal_options_for_inheritance
           This returns a blacklist of options that can not be overridden in a subclass's attribute
           definition.

           This exists to allow a custom metaclass to change or add to the list of options which can not be
           changed.

       $attr->type_constraint
           Returns the Moose::Meta::TypeConstraint object for this attribute, if it has one.

       $attr->has_type_constraint
           Returns true if this attribute has a type constraint.

       $attr->verify_against_type_constraint($value)
           Given a value, this method returns true if the value is valid for the attribute's type
           constraint. If the value is not valid, it throws an error.

       $attr->handles
           This returns the value of the "handles" option passed to the constructor.

       $attr->has_handles
           Returns true if this attribute performs delegation.

       $attr->is_weak_ref
           Returns true if this attribute stores its value as a weak reference.

       $attr->is_required
           Returns true if this attribute is required to have a value.

       $attr->is_lazy
           Returns true if this attribute is lazy.

       $attr->is_lazy_build
           Returns true if the "lazy_build" option was true when passed to the constructor.

       $attr->should_coerce
           Returns true if the "coerce" option passed to the constructor was true.

       $attr->should_auto_deref
           Returns true if the "auto_deref" option passed to the constructor was true.

       $attr->trigger
           This is the subroutine reference that was in the "trigger" option passed to the constructor, if
           any.

       $attr->has_trigger
           Returns true if this attribute has a trigger set.

       $attr->documentation
           Returns the value that was in the "documentation" option passed to the constructor, if any.

       $attr->has_documentation
           Returns true if this attribute has any documentation.

       $attr->applied_traits
           This returns an array reference of all the traits which were applied to this attribute. If none
           were applied, this returns "undef".

       $attr->has_applied_traits
           Returns true if this attribute has any traits applied.

BUGS
       See "BUGS" in Moose for details on reporting bugs.

AUTHOR
       Moose is maintained by the Moose Cabal, along with the help of many contributors. See "CABAL" in
       Moose and "CONTRIBUTORS" in Moose for details.

COPYRIGHT AND LICENSE
       This software is copyright (c) 2012 by Infinity Interactive, Inc..

       This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5
       programming language system itself.



perl v5.16.2                                     2012-09-19                        Moose::Meta::Attribute(3)