Mouse::Meta::Attribute - The Mouse attribute metaclass
This document describes Mouse version v2.5.6
This is a meta object protocol for Mouse attributes, which is a subset of
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
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
- "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
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.
Checks that the given value passes this attribute's type constraint. Returns
"true" on success, otherwise "confess"es.
Creates a new attribute in the owner class, inheriting options from parent
classes. Accessors and helper methods are installed. Some error checking is
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