NAME Object::Pad::FieldAttr::Final - declare Object::Pad fields readonly after construction SYNOPSIS use Object::Pad; use Object::Pad::FieldAttr::Final; class Rectangle { field $width :param :reader :Final; field $height :param :reader :Final; field $area :reader :Final; ADJUST { $area = $width * $height; } } DESCRIPTION This module provides a third-party field attribute for Object::Pad-based classes, which declares that the field 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 field 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. FIELD ATTRIBUTES :Final field $name :Final ...; field $name :Final ... = DEFAULT; Declares that the field 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 field variable. field $x :Final; ADJUST { $x = 123; } # this is permitted method m { $x = 456; } # this will fail Note that this is only a shallow readonly setting; if the field variable contains a reference to a data structure, that structure itself remains mutable. field $aref :Final; ADJUST { $aref = []; } method more { push @$aref, "another"; } # this is permitted AUTHOR Paul Evans <leonerd@leonerd.org.uk>