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.\" ========================================================================
.\"
.IX Title "Mouse::Meta::Attribute 3pm"
.TH Mouse::Meta::Attribute 3pm "2020-11-09" "perl v5.32.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
Mouse::Meta::Attribute \- The Mouse attribute metaclass
.SH "VERSION"
.IX Header "VERSION"
This document describes Mouse version v2.5.10
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This is a meta object protocol for Mouse attributes,
which is a subset of Moose::Meta::Attribute.
.SH "METHODS"
.IX Header "METHODS"
.ie n .SS """new(%options) \-> Mouse::Meta::Attribute"""
.el .SS "\f(CWnew(%options) \-> Mouse::Meta::Attribute\fP"
.IX Subsection "new(%options) -> Mouse::Meta::Attribute"
Instantiates a new Mouse::Meta::Attribute. Does nothing else.
.PP
It adds the following options to the constructor:
.ie n .IP """is => \*(Aqro\*(Aq, \*(Aqrw\*(Aq, \*(Aqbare\*(Aq""" 4
.el .IP "\f(CWis => \*(Aqro\*(Aq, \*(Aqrw\*(Aq, \*(Aqbare\*(Aq\fR" 4
.IX Item "is => ro, rw, bare"
This provides a shorthand for specifying the \f(CW\*(C`reader\*(C'\fR, \f(CW\*(C`writer\*(C'\fR, or
\&\f(CW\*(C`accessor\*(C'\fR names. If the attribute is read-only ('ro') then it will
have a \f(CW\*(C`reader\*(C'\fR method with the same attribute as the name.
.Sp
If it is read-write ('rw') then it will have an \f(CW\*(C`accessor\*(C'\fR method
with the same name. If you provide an explicit \f(CW\*(C`writer\*(C'\fR for a
read-write attribute, then you will have a \f(CW\*(C`reader\*(C'\fR with the same
name as the attribute, and a \f(CW\*(C`writer\*(C'\fR with the name you provided.
.Sp
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.
.ie n .IP """isa => Type""" 4
.el .IP "\f(CWisa => Type\fR" 4
.IX Item "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.
.Sp
This option can also accept a Moose::Meta::TypeConstraint object.
.Sp
If you \fIalso\fR provide a \f(CW\*(C`does\*(C'\fR option, then your \f(CW\*(C`isa\*(C'\fR option must
be a class name, and that class must do the role specified with
\&\f(CW\*(C`does\*(C'\fR.
.ie n .IP """does => Role""" 4
.el .IP "\f(CWdoes => Role\fR" 4
.IX Item "does => Role"
This is short-hand for saying that the attribute's type must be an
object which does the named role.
.Sp
\&\fBThis option is not yet supported.\fR
.ie n .IP """coerce => Bool""" 4
.el .IP "\f(CWcoerce => Bool\fR" 4
.IX Item "coerce => Bool"
This option is only valid for objects with a type constraint
(\f(CW\*(C`isa\*(C'\fR). If this is true, then coercions will be applied whenever
this attribute is set.
.Sp
You can make both this and the \f(CW\*(C`weak_ref\*(C'\fR option true.
.ie n .IP """trigger => CodeRef""" 4
.el .IP "\f(CWtrigger => CodeRef\fR" 4
.IX Item "trigger => CodeRef"
This option accepts a subroutine reference, which will be called after
the attribute is set.
.ie n .IP """required => Bool""" 4
.el .IP "\f(CWrequired => Bool\fR" 4
.IX Item "required => Bool"
An attribute which is required must be provided to the constructor. An
attribute which is required can also have a \f(CW\*(C`default\*(C'\fR or \f(CW\*(C`builder\*(C'\fR,
which will satisfy its required-ness.
.Sp
A required attribute must have a \f(CW\*(C`default\*(C'\fR, \f(CW\*(C`builder\*(C'\fR or a
non\-\f(CW\*(C`undef\*(C'\fR \f(CW\*(C`init_arg\*(C'\fR
.ie n .IP """lazy => Bool""" 4
.el .IP "\f(CWlazy => Bool\fR" 4
.IX Item "lazy => Bool"
A lazy attribute must have a \f(CW\*(C`default\*(C'\fR or \f(CW\*(C`builder\*(C'\fR. When an
attribute is lazy, the default value will not be calculated until the
attribute is read.
.ie n .IP """weak_ref => Bool""" 4
.el .IP "\f(CWweak_ref => Bool\fR" 4
.IX Item "weak_ref => Bool"
If this is true, the attribute's value will be stored as a weak
reference.
.ie n .IP """auto_deref => Bool""" 4
.el .IP "\f(CWauto_deref => Bool\fR" 4
.IX Item "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.
.ie n .IP """lazy_build => Bool""" 4
.el .IP "\f(CWlazy_build => Bool\fR" 4
.IX Item "lazy_build => Bool"
Setting this to true makes the attribute lazy and provides a number of
default methods.
.Sp
.Vb 4
\&  has \*(Aqsize\*(Aq => (
\&      is         => \*(Aqro\*(Aq,
\&      lazy_build => 1,
\&  );
.Ve
.Sp
is equivalent to this:
.Sp
.Vb 7
\&  has \*(Aqsize\*(Aq => (
\&      is        => \*(Aqro\*(Aq,
\&      lazy      => 1,
\&      builder   => \*(Aq_build_size\*(Aq,
\&      clearer   => \*(Aqclear_size\*(Aq,
\&      predicate => \*(Aqhas_size\*(Aq,
\&  );
.Ve
.ie n .SS """associate_method(MethodName)"""
.el .SS "\f(CWassociate_method(MethodName)\fP"
.IX Subsection "associate_method(MethodName)"
Associates a method with the attribute. Typically, this is called internally
when an attribute generates its accessors.
.PP
Currently the argument \fIMethodName\fR is ignored in Mouse.
.ie n .SS """verify_against_type_constraint(Item) \-> TRUE | ERROR"""
.el .SS "\f(CWverify_against_type_constraint(Item) \-> TRUE | ERROR\fP"
.IX Subsection "verify_against_type_constraint(Item) -> TRUE | ERROR"
Checks that the given value passes this attribute's type constraint. Returns \f(CW\*(C`true\*(C'\fR
on success, otherwise \f(CW\*(C`confess\*(C'\fRes.
.ie n .SS """clone_and_inherit_options(options) \-> Mouse::Meta::Attribute"""
.el .SS "\f(CWclone_and_inherit_options(options) \-> Mouse::Meta::Attribute\fP"
.IX Subsection "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.
.ie n .SS """get_read_method_ref"""
.el .SS "\f(CWget_read_method_ref\fP"
.IX Subsection "get_read_method_ref"
.ie n .SS """get_write_method_ref"""
.el .SS "\f(CWget_write_method_ref\fP"
.IX Subsection "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.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Moose::Meta::Attribute
.PP
Class::MOP::Attribute