Creation

Moose::Meta::Attribute->new($name, %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:

$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->role_attribute

Returns the Moose::Meta::Role::Attribute object from which this attribute was created, if any. This may return "undef".

$attr->has_role_attribute

Returns true if this attribute has an associated role attribute.

$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.