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NAME

Object::Pad::SlotAttr::Final - declare Object::Pad slots readonly after construction

SYNOPSIS

class Rectangle {
has $width :param :reader :Final;
has $height :param :reader :Final;
has $area :reader :Final;
ADJUST {
$area = $width * $height;
}
}

DESCRIPTION

This module provides a third-party slot attribute for Object::Pad-based classes, which declares that the slot it is attached to shall be set as readonly when the constructor returns, disallowing further modification to it.

WARNING The ability for Object::Pad to take third-party slot attributes is still new and highly experimental, and subject to much API change in future. As a result, this module should be considered equally experimental.

SLOT ATTRIBUTES

:Final

has $slot :Final ...;
has $slot :Final ... = DEFAULT;

Declares that the slot variable will be set readonly at the end of the constructor, after any assignments from :param declarations or ADJUST blocks. At this point, the value cannot otherwise be modified by directly writing into the slot variable.

has $slot :Final;
ADJUST { $slot = 123; } # this is permitted
method m { $slot = 456; } # this will fail

Note that this is only a shallow readonly setting; if the slot variable contains a reference to a data structure, that structure itself remains mutable.

has $aref :Final;
ADJUST { $aref = []; }
method more { push @$aref, "another"; } # this is permitted

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>