NAME

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

DESCRIPTION

This is a subclass of Class::MOP::Attribute with Moose specific extensions.

For the most part, the only time you will ever encounter an instance of this class is if you are doing some serious deep introspection. To really understand this class, you need to refer to the Class::MOP::Attribute documentation.

METHODS

Overridden methods

These methods override methods in Class::MOP::Attribute and add Moose specific features. You can safely assume though that they will behave just as Class::MOP::Attribute does.

new

clone

does

initialize_instance_slot

install_accessors

install_delegation

accessor_metaclass

get_value

set_value

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

Attribute (x) does not pass the type constraint (Int) with 'fourty-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 with a throw_error.

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::Recipe4 for an example.

Additional Moose features

Moose attributes support type-constraint checking, weak reference creation and type coercion.

throw_error

Delegates to associated_class or Moose::Meta::Class if there is none.

interpolate_class_and_new

interpolate_class

When called as a class method causes interpretation of the metaclass and traits options.

clone_and_inherit_options

This is to support the has '+foo' feature, it clones an attribute from a superclass and allows a very specific set of changes to be made to the attribute.

legal_options_for_inheritance

Whitelist with options you can change. You can overload it in your custom metaclass to allow your options be inheritable.

has_type_constraint

Returns true if this meta-attribute has a type constraint.

type_constraint

A read-only accessor for this meta-attribute's type constraint. For more information on what you can do with this, see the documentation for Moose::Meta::TypeConstraint.

has_handles

Returns true if this meta-attribute performs delegation.

handles

This returns the value which was passed into the handles option.

is_weak_ref

Returns true if this meta-attribute produces a weak reference.

is_required

Returns true if this meta-attribute is required to have a value.

is_lazy

Returns true if this meta-attribute should be initialized lazily.

NOTE: lazy attributes, must have a default or builder field set.

is_lazy_build

Returns true if this meta-attribute should be initialized lazily through the builder generated by lazy_build. Using lazy_build => 1 will make your attribute required and lazy. In addition it will set the builder, clearer and predicate options for you using the following convention.

   #If your attribute name starts with an underscore:
   has '_foo' => (lazy_build => 1);
   #is the same as
   has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', builder => '_build__foo');
   # or
   has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', default => sub{shift->_build__foo});

   #If your attribute name does not start with an underscore:
   has 'foo' => (lazy_build => 1);
   #is the same as
   has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', builder => '_build_foo');
   # or
   has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', default => sub{shift->_build_foo});

The reason for the different naming of the builder is that the builder method is a private method while the clearer and predicate methods are public methods.

NOTE: This means your class should provide a method whose name matches the value of the builder part, in this case _build__foo or _build_foo.

should_coerce

Returns true if this meta-attribute should perform type coercion.

should_auto_deref

Returns true if this meta-attribute should perform automatic auto-dereferencing.

NOTE: This can only be done for attributes whose type constraint is either ArrayRef or HashRef.

has_trigger

Returns true if this meta-attribute has a trigger set.

trigger

This is a CODE reference which will be executed every time the value of an attribute is assigned. The CODE ref will get two values, the invocant and the new value. This can be used to handle basic bi-directional relations.

documentation

This is a string which contains the documentation for this attribute. It serves no direct purpose right now, but it might in the future in some kind of automated documentation system perhaps.

has_documentation

Returns true if this meta-attribute has any documentation.

applied_traits

This will return the ARRAY ref of all the traits applied to this attribute, or if no traits have been applied, it returns undef.

has_applied_traits

Returns true if this meta-attribute has any traits applied.

BUGS

All complex software has bugs lurking in it, and this module is no exception. If you find a bug please either email me, or add the bug to cpan-RT.

AUTHOR

Stevan Little <stevan@iinteractive.com>

Yuval Kogman <nothingmuch@woobling.com>

COPYRIGHT AND LICENSE

Copyright 2006-2008 by Infinity Interactive, Inc.

http://www.iinteractive.com

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