NAME

    Object::Pad::FieldAttr::Final - declare Object::Pad fields readonly
    after construction

SYNOPSIS

       use Object::Pad;
       use Object::Pad::FieldAttr::Final;
    
       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 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

       has $field :Final ...;
       has $field :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.

       has $field :Final;
    
       ADJUST { $field = 123; }    # this is permitted
    
       method m { $field = 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.

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

AUTHOR

    Paul Evans <leonerd@leonerd.org.uk>