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Mouse::Meta::Attribute - The Mouse attribute metaclass


This document describes Mouse version v2.4.10


This is a meta object protocol for Mouse attributes, which is a subset of Moose::Meta::Attribute.


new(%options) -> Mouse::Meta::Attribute

Instantiates a new Mouse::Meta::Attribute. Does nothing else.

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.

This option is not yet supported.

coerce => Bool

This option is only valid for objects with a type constraint (isa). 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 => CodeRef

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',


Associates a method with the attribute. Typically, this is called internally when an attribute generates its accessors.

Currently the argument MethodName is ignored in Mouse.

verify_against_type_constraint(Item) -> TRUE | ERROR

Checks that the given value passes this attribute's type constraint. Returns true on success, otherwise confesses.

clone_and_inherit_options(options) -> Mouse::Meta::Attribute

Creates a new attribute in the owner class, inheriting options from parent classes. Accessors and helper methods are installed. Some error checking is done.



Returns the subroutine reference of a method suitable for reading or writing the attribute's value in the associated class. These methods always return a subroutine reference, regardless of whether or not the attribute is read- or write-only.