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>