---
name: "Mouse::Meta::Attribute"
section: "3pm"
platform: "linux"
package: "perl-mouse"
version: "2.6.2-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/Mouse::Meta::Attribute"
---

# Mouse::Meta::Attribute(3pm)

The Mouse attribute metaclass

## NAME

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

## VERSION

This document describes Mouse version v2.6.2

## DESCRIPTION

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

## METHODS

### "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',
    );
  ```

### associate\_method(MethodName)

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 `"confess"`es.

### "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.

### "get\_read\_method\_ref"

### "get\_write\_method\_ref"

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.

## SEE ALSO

Moose::Meta::Attribute

Class::MOP::Attribute